Contacts which can be forced into metallized holes of a printed circuit card are widely used at the present time to make solderless connections. They generally contain a first end portion designed to pass through the hole and project beyond one of the faces of the card, when the contact is in an insertion position, and a second end portion designed to project beyond the other face of the card. These two ends are joined by an intermediate portion, the function of which is ensure the electrical connection of the contact with the metallized interior surface of the hole and at the same time its mechanical retention in the hole.
A number of contacts include an indeformable prismatic intermediate portion having a rectangular or square section. On the insertion of such a contact, the edges of the intermediate portion, which extend parallel to the longitudinal axis of the contact or to its direction of insertion in the hole, dig themselves in the lined wall of the hole, thus forming gastight bonds which retard corrosion at the contact surfaces.
Those contacts present, however, a number of disadvantages. In particular, on their insertion into an opening which is too small, considerable forces develop in the axial direction which can tear away the lining or intermediate conductive layers, in the case of use of multi-layer circuits. On the other hand, if the size of the opening is too great, the axial retention of the contact through friction of the contact on the lining will be poor and may further deteriorate due to mechanical stresses (such as vibrations, or axial stresses exerted on either end of the contact or due to) or thermal stresses. It is clear that the use of this type of contact requires maintaining very strict dimensional tolerances on the printed circuit opening, which are difficult to obtain by electroplating methods. It is to be noted that when openings do not have perfectly round sections, the same contact will be retained better or worse according to whether the diagonals of its section correspond to a greater or lesser diameter of the opening measured in the direction of those diagonals. Furthermore, the radial stresses exerted by the median port on the lining are exerted in two diagonal directions, and this irregular distribution can lead to cracking of the lining.
There are still other contacts in which the intermediate portion is elastically deformable in a radial direction, which makes it possible, in theory, to reduce the dimensional tolerances of the lined holes which are to receive them. However, the gastightness of the contact surfaces is maintained only by providing absolutely optimal conditions of tolerance and use. It is also to be noted that the contact surface between the median part and the wall of the lining is never made over the entire height of that intermediate portion, which can lead to an unstable mechanical retention of the contact. Finally, the axial stresses and also the rotational stresses applied to the ends of the contact can be only imperfectly absorbed by the effect of friction on the wall of the lining.